[TECH DEBT] Refactor errors

[rob-maron]

This PR:

Is the first step towards getting better logging/errors.

• Switches everything from snafu to thiserror. This should get rid of the errors akin to "Libp2p-specific errors" and "Error in the Kademlia DHT"
• Deduplicates some warnings/errors. Some errors will log and then return, where they got logged a second time. I plan to do more of this in a coming PR, along with adding more context where necessary
• Removes unused errors and error variants

This PR does not:

• Refine log levels
• Change things to use anyhow anywhere
• Apart from formatting, does not touch existing, in-use log messages (besides adding context) or log types.

Key places to review:

The only really important errors are the HotShot ones, so everything mentioning HotShotError

How to test this PR:

I've run this in the sequencer. I didn't see any unused error variants or anything